The present invention relates to apparatus and method for processing a steering angle signal generated from an absolute type steering angle sensor which detects a rotational angle of a steering system of a motor vehicle such as an automobile and generates the steering angle signal in response to the detected rotational angle.
In a four-wheel motor vehicle which is capable of controlling a rotational steering angle of rear wheels in response to a steering angle of front wheels, there is conventionally known as a steering angle detecting system for the front wheel, a so-called "absolute type" steering angle sensor. Such a steering angle sensor comprises a small gear coupled with a steering shaft and a potentiometer whose output voltage is changed in response to the revolution of a large gear meshed with the small gear. The sensor detects the rotational angle of the steering shaft in response to the output voltage of the potentiometer (the Japanese Utility Model Laid-Open (KOKAI) Publication No. 62-14309).
The applicant of the present application has filed Japanese Utility Model Application No. 1-26899 (26899/1989), which discloses a clutch mechanism disposed between the steering angle sensor and a gear shaft of a driven gear meshed with a driving gear mounted to the steering shaft to exactly adjust 0 point of a steering wheel angle to an actual central point of the steering angle sensor by a push button. In this case where the absolute type steering angle sensor is utilized as the rotational steering angle is optionally detected.
However, in the mechanism described above, a minute adjustment is required to exactly meet the 0.degree. steering wheel angle point with the central point of the steering sensor. There also remains a problem of the deviation between the 0.degree. steering wheel angle point and the central point of the steering sensor which may be caused by the wear of tires or a suspension bushing by long use, or by a sudden change of the bilateral balancing condition against the load exerted on the vehicle, or due to the tire exchanging operation, even if the 0.degree. steering wheel angle point and the central point of the steering sensor be once exactly adjusted so as to meet with each other.